An erect image 2.0 cm high is formed 12 cm from a lens, the object being 0.5 cm high. Find the focal length of the lens.
Height of image = 2 cm
Image distance = 12 cm
Height of object= 0.5 cm
M = height of image/ height of object = 2/0.5 =- 4
M = v/u
-4 = 12/u
u =- 3 cm
using lens formula,
f = + 4.0 cm
20